Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from wind using known airfoil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. More specifically, each rotor blade is typically secured at its root end and spans radially outboard to a free tip end. The leading edge of the rotor blade connects the forward-most points of the blade that first contact the air. The trailing edge of the blade is where airflow that has been separated by the leading edge rejoins after passing over the suction and pressure surfaces of the blade. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
In order to prevent damage to the blades, wind turbines often include a controller to manage wind turbine operation, such as start-up/shut-down, power output, power curve measurement, nacelle yaw, and blade pitch, in response to wind speed and/or other controller inputs. Inputs to the controller typically include various wind characteristics such as wind speed and direction taken from an anemometer with a vane. The anemometer measurements that are made using these instruments are subject to a variety of effects that cause inaccuracies, including the turbulent effect of the rotating blades into and out of the fluid flow path of the anemometer on the nacelle. Consequently, an additional meteorological, or “met” mast is sometimes arranged a suitable distance upwind of the wind turbine for taking “freestream” wind speed and direction measurements which approximate the actual wind speed and direction that would have been measured at the turbine location had the turbine not been present.
The relationship between the measured wind speed on the turbine nacelle and the actual freestream wind speed is sometimes referred to as the “nacelle-to-freestream transfer function,” or simply the “transfer function.” It is well known in the art that the transfer function between the measured wind speed on the nacelle and the freestream wind speed depends on multiple variables, including but not limited to, the mounting location of the anemometer, blade design, and/or the pitch angle of each of the rotor blades. Further, U.S. Pat. No. 7,861,583 entitled “Wind Turbine Anemometry Compensation” filed on Jan. 17, 2008, which is incorporated herein by reference in its entirety, discloses a system for estimating a freestream wind characteristic for a wind turbine having a rotor.
In addition, the rotor blades of the wind turbine are desirably installed at a certain pitch angle referenced from a “zero” location. If the zero reference location is inaccurate, however, the pitch angle of each of the rotor blades may be offset causing a rotor imbalance or asymmetry during operation of the wind turbine. Further, even if the rotor blades are installed at the proper pitch angle, the angle of one or more of the blades may become offset during normal operation, e.g. due to various wind conditions. Rotor asymmetry can cause undesirable wear and tear and/or loading on the wind turbine as well as inefficient operation.
As such, it is desirable to detect rotor asymmetry such that the imbalance can be corrected and resulting loads of the wind turbine and/or power loss can be reduced. Conventional methods for detecting rotor asymmetry include personnel climbing uptower to install one or more reference spots or locations on the nacelle. A ground camera then takes pictures of the spot locations to evaluate the position of each of the rotor blades. Based on the locations, the pitch angles may be adjusted by the wind turbine controller. Such methods, however, can be time consuming, expensive, and even dangerous.
Thus, an improved system and method for detecting rotor asymmetry is desired in the art. Accordingly, the present disclosure is directed to a system and method for detecting rotor asymmetry based on one or more anemometer measurements.